Chair base



FIG. 1 is a side view of a chair base showing our new design;

FIG. 2 is another side view thereof;

FIG. 3 is another side view thereof;

FIG. 4 is another side view thereof; and,

FIG. 5 is a top view thereof.

The side views illustrate various degrees of rotation of the chair base. 

The ornamental design for a chair base, as shown and described. 